Self-supporting cables and an apparatus and methods for making the same

ABSTRACT

Cables and an apparatus and methods for making cables having at least one messenger section, transmission sections, and at least two series of connecting webs. At least one series of webs can be intermittently formed. The messenger section can include a messenger wire for supporting the cable, and the transmission sections can include electrical/electronic and/or optical transmission components. A method of making cables may include the steps of pulling cable components through a melt cavity having a molten jacketing material therein; defining at least three cable sections by coating the cable components with the molten jacketing material; monolithically forming at least two series of connecting webs made of the molten jacketing material between each cable section during a web-forming mode; and defining intermittent webs by forming longitudinal gaps between the webs of at least one of the series of webs during a gap-forming mode by switching between the web-forming and gap-forming modes with respect to the at least one series of webs. The apparatus includes a melt cavity associated with a die orifice having web-forming sections, and gap forming parts associated with the web-forming sections, the gap forming parts being operative to block the flow of the cable jacketing material for forming gaps defining the webs.

RELATED APPLICATIONS

The present application is a Divisional of U.S. Ser. No. 09/344,151filed on Jun. 24, 1999 now U.S. Pat. No. 6,563,990, which is aContinuation-In-Part of Ser. No. 09/280,503 filed Mar. 30, 1999, nowU.S. Pat. No. 6,188,822, which is a Continuation-In-Part of Ser. No.09/102,392, filed Jun. 22, 1998, now U.S. Pat. No. 6,188,821.

FIELD OF INVENTION

The present invention relates to cables, and an apparatus and methodsfor making cables, that can include at least one optical fiber.

BACKGROUND OF THE INVENTION

Fiber optic cables include at least one optical fiber that can transmittelecommunication information, for example, voice, data, and videoinformation. Self-supporting fiber optic cables are designed for aerialapplications and typically include a messenger wire and a core sectionhaving conductors therein that may be solely optical or a combination ofoptical and electrical conductors. Self-supporting fiber optic cables ofthe FIG. 8 type may be characterized into two general categories,namely, self-supporting cables with a core section having no excesslength relative to the messenger wire, and self-supporting cables havinga core section having an over-length, typically about 0.2%, relative tothe messenger wire. Examples of self-supporting cables having no coresection over-length are disclosed in U.S. Pat. Nos. 4,449,012,4,763,983, 5,095,176, and 5,371,823. Examples of self-supporting cableshaving a core section over-length are disclosed in U.S. Pat. Nos.4,662,712 and 4,883,671.

When installed in a self-supporting application, self-supporting cablesmay experience a high degree of tension. The messenger wire bears mostof the tension, thereby supporting the core section, and protecting theoptical fibers in the core section from high tensile forces. As tensionacts on the messenger wire, however, the messenger wire tends toelongate, which results in an elongation of the core section. Elongationof the core section of a self-supporting fiber optic cable not having anover-length may cause attenuation losses and/or can compromisemechanical reliability of the optical fibers. On the other hand, wherethe core section of a self-supporting cable having a core sectionover-length is elongated, the elongation is, up to the amount ofexisting over-length of the core section, advantageously taken up by theover-length in the core section whereby the core section may beelongated without potentially causing strain and/or attenuation in theoptical fibers.

The extruder cross-head used to manufacture self-supporting cables canbe configured to define continuous or intermittent webs for connectingcable sections, for example, as disclosed in U.S. Pat No. 4,467,138.Web-forming extruder cross-heads include a single plunger, e.g., as isdisclosed in JP-46-38748 and JP-8-75969. As disclosed in JP-8-75969, forexample, the extruder head includes a melt cavity with a moltenjacketing material therein. As the messenger wires and core translatethrough the melt cavity they are coated with the molten jacketingmaterial. As the messenger wires and core exit the extruder head, a dieorifice determines the peripheral shape of the cable jacket therearound,and the orifice includes a web-forming area for the formation of webs.The plunger operates by moving into a blocking position in the dieorifice between cable sections, physically blocking the molten jacketingmaterial from forming the web. The plunger is reciprocated in and out ofthe blocking position so that the webs are formed intermittently, spacedby longitudinal gaps.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a cross sectional view of a fiber optic cable according to thepresent invention taken at line 1—1 of FIG. 7.

FIG. 2 is a cross sectional view of a fiber optic cable according to thepresent invention.

FIG. 3 is a cross sectional view of a fiber optic cable according to thepresent invention.

FIG. 4 is an isometric view of a fiber optic cable according to thepresent invention.

FIG. 5 is a cross sectional view of the fiber optic cable of FIG. 4.

FIG. 6 is a schematic view of an exemplary application for fibers opticcables according to the present invention.

FIG. 7 is an isometric view of an extruder head according to the presentinvention for use in manufacturing fiber optic cables according to thepresent invention.

FIG. 8 is a front view of the extruder cross-head of FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-5, exemplary embodiments of fiber optic cables20,40,60,80 according to the present invention will be described. Fiberoptic cable 20 (FIGS. 1 and 7) can be a self-supporting cable that iscomposed of cable sections, for example, a messenger section 22 andtransmission sections 26 and 28. Each cable section preferably comprisesa portion of a cable jacket 21 having webs 24 that connect cablesections 22,26,28 together. Messenger section 22 preferably comprisesnon-metallic and/or metallic strength members, for example, aramid orfiberglass yarns, glass reinforced plastic rods, and/or a steelmessenger wire 23. Transmission section 26 preferably comprises at leastone transmission component, for example, an electrical/electroniccomponent 27. Transmission component 27 can be, for example, a twistedpair of electrical wires that are preferably surrounded by a layer ofstrength members 25. Transmission component 27 preferably performs, forexample, a data or power transmission function. Transmission section 28preferably includes at least one optical fiber, for example, in anoptical unit 30. Optical unit 30 preferably comprises at least onesingle mode, multi-mode, or multi-core optical fiber, and may besurrounded by a layer of strength members 29. Strength members 25,29preferably comprise filaments, for example, aramid strength members withor without a coating of water blocking grease, or a superabsorbentpowder or matrix coating. Alternatively, in lieu of strength members25,29 the transmission components can be generally surrounded by a waterblocking grease. Jacket 21 preferably is formed of, for example, PVC,FRPE, PE, or a UV curable resin, e.g., an acrylate. Webs 24 arepreferably intermittently formed along the length of the cable and aresized to be ripped manually, or with tools, for separating sections22,26,28.

Fiber optic cables according to the present invention can include anysuitable kind or number of optical transmission components for thetransmission of telecommunications information, and/orelectrical/electronic transmission components for transmittingtelecommunications information and/or power. For example, fiber opticcable 40 (FIG. 2) includes a transmission section 46 having more thanone pair of twisted wires 47. Fiber optic cable 60 (FIG. 3) preferablyincludes a transmission section 66 comprising a composite ofpower-transmitting conductors 67 disposed about at least one coaxialelectrical conductor 68, and fiber optic cable 80 (FIGS. 4-5) preferablyincludes a transmission section 86 including copper clad steel strengthmembers 87.

Fiber optic cables according to the present invention can include anysuitable kind or number of optical transmission components. For example,fiber optic cable 40 can include a transmission section 48 having tightbuffered optical fibers 50. Fiber optic cable 60 can include a loosetube core comprising a central member 71, an optical component 70 havingloose buffered optical fibers 72, a core wrap or water swellable tape74, and strength members 75. As a further illustration, fiber opticcable 80 can include a transmission section 88 having an opticalcomponent 90 including, for example, a mono-tube with loose and/orbundled optical fibers 91 therein. Cable sections 26,46,66,86 caninclude at least one optical transmission component, and cable sections28,48,68,88 can include one or more electrical/electronic transmissioncomponents.

In other aspects of the present invention, each cable jacket 21,41,61,81can include, for example, intermittent webs 24 or 81 (FIGS. 1, 4-6, and7), continuous webs 44 (FIG. 2), or a combination of a intermittent andcontinuous webs 63,64 (FIG. 3). Webs 24,44,63,64,84 can be sized forease of manual or tool-assisted separation of the respective cablesections. The web thickness can be less than about 75% of thediameter/thickness of the largest cable section, preferably less thanabout 50%, and most preferably less than about 25% thereof.

As an illustration, fiber optic cables of the present invention can beused in a fiber-to-the-home (FTTH) application (FIG. 6). In theexemplary application, a craftsman would separate messenger section 22from transmission section 26 by tearing or snipping webs 24. Next,strength member 23 of messenger section 22 is mechanically attached to,for example, a house. Transmission sections 26,28 are then dropped to anetwork interface device N containing, for example, a modem that can bepowered by electrical components 27 and optically interconnected withoptical transmission component 30.

Additional aspects of the present invention include methods and anapparatus for making fiber optic cables according to the presentinvention. With reference to FIGS. 7-8, an exemplary apparatus andmanufacturing process will be described with exemplary reference tofiber optic cable 20. According to the present invention, extrudercross-head 100 can be used to extrude jacket 21 and webs 24. Morespecifically, extruder cross-head 100 extrudes molten jacketing materialthat forms jacket 21 and webs 24 as cable 20 moves along the directionof arrow A (FIG. 7). Extruder cross-head 100 preferably includes a body101 with a melt cavity therein. The melt cavity receives moltenjacketing material from an extruder (not shown), messenger wire 23,strength members 25 with transmission components 27, and strengthmembers 29 with optical unit 30 therein. Extruder cross-head 100preferably includes a die orifice 102 having web forming sections 104(FIG. 8), a messenger profile area 105, and transmission profile areas107. Transmission profile areas 107 apply the jacketing material tostrength members 25,29 by, for example, a tube-on application combinedwith a draw down vacuum. Messenger profile area 105 applies thejacketing material to messenger wire 23 by, for example, pressureextrusion.

Extruder head 100 preferably includes at least one gap forming part thatperforms a gap forming function, for example, a plunger 106 that ismovably mounted to body 101 for reciprocating action along the directionof arrow B (FIG. 7). Extruder cross-head 100 can include at least twoplungers 106 operative to reciprocate between blocking and non-blockingpositions with respect to web forming sections 104. At least one plunger106 can include a radius 106 a (FIG. 8), adjacent to messenger profilearea 105, complementing the outer surface of the messenger portion ofjacket 21. The advance of plungers 106 can be stopped by respectivedowel pins 111 fastened thereto. The tip ends of plungers 106 can bereceived in respective recesses 108 of body 101 (FIG. 8). Moreover, theplungers can be located on opposed sides of die orifice 102, forexample, one on top and the other on the bottom (not shown). The motionof plungers 106 can be operatively interlocked to move in unison, can beoperated independently of each other, and/or can be timed to be at thesame or different web forming positions to suit the desired web formingneed. Extruder cross-heads according to the present invention mayinclude more than one pressure regulating device.

The present invention preferably includes a pressure regulating device120 (FIGS. 5 and 6) attached to extruder cross-head 100 for regulatingthe pressure in the melt cavity, as described in U.S. Ser. No.09/280,503 incorporated by reference herein. Pressure regulating device120 is operative to keep the melt cavity pressure substantiallyconstant, i.e., there will be substantially no pressure fluctuation inthe melt cavity as plungers 106 are reciprocated between the blocking,i.e., gap-forming, and non-blocking, i.e., web forming, positions.

As plungers 106 are switched between web-forming and gap-forming modes,pressure-regulating device 120 is preferably controlled in synctherewith to assure uniform jacket thickness. For example, plungers 106and pressure regulating device 120 are preferably operatively connectedto motion actuating devices, for example, dual acting pneumaticcylinders (not shown). The pneumatic cylinders can be operativelyassociated with a pneumatic solenoid 112, shown schematically in FIG. 7,that can simultaneously control the positions of the motion actuatingdevices along the directions of arrows B and C. Solenoid 112 can becontrolled by, for example, a conventional programmable logic controller(PLC) (not shown) that interfaces with a cable length counter (notshown) and is programmed to switch the solenoid based on cable lengthinformation received from the length counter. The PLC can also beprogrammed to change the length of webs 24 and/or the longitudinal gapsbetween webs by driving plungers 106 accordingly. In addition, the PLCcan be programmed to have both plungers in a non-intermittentweb-forming mode for forming a cable with continuous webs (FIG. 2), oneof the plungers can be operated to make intermittent webs with the otherplunger forming a continuous web (FIG. 3), or both plungers 106 can bedriven to form intermittent webs (FIGS. 1, 4-6, and 7). When solenoid112 is switched between web-forming and longitudinal gap-forming modesby the PLC, the motion actuating devices can act in parallel to causeplungers 106 and pressure regulating device 120 to be switched at thesame time. Plungers 106 can be controlled to suit the desired cabledesign and materials cost requirements. For example, where both plungers106 are operated to form intermittent webs, the webs can be spaced atgenerally the same axial locations along the cable, the respectivelocations of the webs can have a staggered spacing, and/or thesizes/thickness of the webs can be the same or different.

An exemplary operation of extruder cross-head 100 for applying jacket 21will now be described. Continuing the example of cable 20, the methodaccording to the present invention preferably comprises the steps of:pulling messenger wire 23, strength members 25 with transmissioncomponents 27, and strength members 29 with optical component 30 thereinthrough a melt cavity having a molten jacketing material therein;defining messenger section 22 and transmission sections 26,28 by coatingthe messenger wire 23, strength members 25, and strength members 29 withthe molten jacketing material; and forming webs between at leastrespective cable sections 22,26,28. Moreover, any of the cable sectionscan be formed with an over-length, for example, by conventionalparameter control methods including the application of tension orvelocity differential methods. Application of tension to cablecomponents can stretch the components relative to the messenger wire sothat after release of the tension the stretched components relax andhave an over-length relative to the messenger wire. In the velocitydifferential method, the cable components are fed at a faster speedrelative to the messenger wire thereby creating an over-length withrespect thereto. Transmission sections could have different amounts ofover-length relative to each other and with respect to the messengerwire.

More specifically, messenger wire 23, strength members 25 withtransmission components 27, and strength members 29 with opticalcomponent 30 therein are moved at suitable velocity and tensionparameters into the melt cavity of body 101. Transition section profilearea 107 applies the jacketing material by a tube-on process includingapplication of a vacuum to draw jacket 21 tightly against strengthmembers 25,29. Messenger profile area 105 applies the jacketing materialto messenger wire 23 by a pressure extrusion process whereby theinterstices between the wire strands are preferably completely filledwith jacketing material. Cable sections 22,26,28 of fiber optic cable 20emerge from the outlet side of extruder cross-head 100 for furtherprocessing down the line. Webs 24 are monolithically and intermittentlyformed as part of jacket 21 during the process. Velocity differentialand/or release of tension on the cable sections can result in anover-length relative to messenger wire 23.

During the web-forming mode of the jacketing process, the moltenjacketing material is expressed into web-forming sections 104 therebyforming webs 24. At this point, solenoid 112 requires the motionactuating devices to position plungers 106 such that the plungers areretracted from web forming sections 104, and pressure regulating device120 is inactive. At this time in the process, the jacketing materialinside the melt cavity experiences an initial melt cavity pressure. Inthe exemplary process, webs 24 are made intermittently along the lengthof fiber optic cable 20. To accomplish this, solenoid 112 is repeatedlyswitched from the web-forming mode to the gap-forming mode and backagain according to a program in the PLC. Webs 24 are formed in more thanone web series between respective cable sections, for example, seriesS1, S2 (FIG. 7), and a web series may include a single continuous web S3(FIG. 2). Specifically, the gap-forming mode requires plungers 106 to bein the blocking position, and pressure regulating device 120 to be in aposition to relieve pressure in the melt cavity by releasing moltenjacketing material for the interval of time that the gaps are beingformed. The purpose of pressure regulating device 120 is to maintain thepressure in the melt cavity at substantially the initial melt cavitypressure during the gap-forming mode. To accomplish this purpose,jacketing material will be released by pressure regulating device 120during formation of the longitudinal gaps. In other words, when plungers106 are in the blocking position and the longitudinal gaps are beingformed, an amount of molten jacketing material can be released bypressure regulating device 120 sufficient to avoid a substantialincrease in melt cavity pressure. The amount of expressed material canbe roughly equal to the volume of material that would fill thelongitudinal gaps if the plunger was not used.

The amount of jacketing compound that is released to avoid the increasein pressure can depend upon process and extruder cross-head variables,to name a few, the physical characteristics of the jacketing material(e.g. viscosity and density), melt cavity temperature and pressure, andproduct line speed. The PLC program controls the intervals of timeduring which the web-forming and gap-forming modes are operative. Thecontrolled release of jacketing material from the melt cavity bypressure regulating device 120 avoids substantial pressure fluctuations.Where the webs are formed continuously pressure regulating device 120need not be activated.

The methods of the present invention can be applied to make fiber opticcables with webs formed continuously, intermittently, or both, and withsubstantially uniform cross sectional jacket thicknesses.

The present invention has been described with reference to the foregoingexemplary embodiments, which embodiments are intended to be illustrativeof the present inventive concepts rather than limiting. Persons ofordinary skill in the art will appreciate that variations andmodifications of the foregoing embodiments may be made without departingfrom the scope of the appended claims. The concepts described herein canbe applied to, for example, opto/electronic composite, buried, indoor,and indoor/outdoor cable applications. The concepts described herein canbe applied to cables including metallic conductors without opticalcomponents, for example, a cable with a twisted pair in one transmissionsection and a coaxial cable in another transmission section. Any cablesection can include an armor layer, more than one messenger section canbe used, and a messenger section can be located adjacent or between anytransmission section. The cable sections preferably have centers thereofgenerally aligned in a plane, or the cable sections can be offset, forexample, the cable sections can be connected in V-shaped, L-shaped ortriangular configurations, e.g., each section can be connected to twoother cable sections, so that at least some of the cable section centersare in a common plane. Flame retardant jacket materials can be selectedto achieve, plenum, riser, or LSZH flame ratings. Water absorbing orblocking substances may be included in any interstice in accordance withapplication requirements. The geometry of the webs shown in the drawingfigures is exemplary, other web geometries may be used, for example,notches, grooves, arcuate surfaces, or any other suitable shape forattaining a balance between strength in connecting the cable sectionsare ease of separability during installation. The methods of the presentinvention can include the steps of forming the messenger section jacketby a tube-on process with a draw down vacuum, and applying thetransmission section jackets by pressure extrusion. Alternatively, thestep of forming the messenger and transmission section jackets caninclude the same method of applying the jacketing material. The gapforming parts can be other than plungers, for example, they can begates, blades, pins, disks, vanes, partitions, or plugs and can beassociated with power or motion transmitting components in lieu of or inaddition to the cylinders, for example, bearings, rocker arms, cams,gears, electrical components, and/or linkages. The cable sections can bemarked according to any suitable marking scheme, for example, indentmarking with or without tape, sequential marking, and/or co-extrusionstriping.

1. A method of making a cable having a cable jacket with webs,comprising the steps of: (a) pulling cable components through a meltcavity having a molten jacketing material therein; (b) defining at leastthree cable sections by coating the cable components with said moltenjacketing material; (c) monolithically forming at least two series ofconnecting webs made of said molten jacketing material between each saidcable section during a web-forming mode; and (d) defining intermittentwebs by forming longitudinal gaps in at least one of said series of websduring gap-forming mode by switching between said web-forming andgap-forming modes.
 2. The method of claim 1, comprising the step ofregulating the pressure of said molten jacketing material to minimizepressure fluctuations during the gap-forming mode.
 3. The method ofclaim 1, the step of forming respective gaps in said at least one seriesof webs being performed by a gap-forming part that blocks the flow ofsaid molten jacketing material.
 4. The method of claim 1, the step offorming said connecting webs being performed by retracting a gap-formingpart from said melt cavity.
 5. The method of claim 1, the step offorming at least one of said cable sections including pressure extrusionof said molten jacketing material.
 6. The method of claim 1, the step offorming at least one of said cable sections including tubing-on anddrawing down said molten jacketing material with a vacuum.
 7. The methodof claim 1, the step of defining intermittent webs by forminglongitudinal gaps comprising forming intermittent webs in at least twoof said series of webs.
 8. A method of making a cable having a cablejacket with webs, comprising the steps of: (a) pulling cable componentsthrough a melt cavity having a molten jacketing material therein; (b)defining at least three cable sections by coating the cable componentswith said molten jacketing material and defining at least one messengercable section for supporting said cable, at least one transmission cablesection comprising at least one optical transmission component, and atleast one transmission cable section comprising at least oneelectrical/electronic transmission component, at least one respectivestrength filament being disposed within each respective transmissioncable section adjacent each said at least one transmission component;and (c) monolithically forming at least two series of connecting websmade of said molten jacketing material between each said cable sectionduring a web-forming mode.
 9. An apparatus for extruding a cablejacketing material, comprising: a melt cavity associated with a dieorifice comprising web-forming sections for forming distinct websbetween cable sections; at least one gap forming part associate with atleast one of said web-forming sections, said gap forming part beingoperative to block the flow of said cable jacketing material for formingwebs between at least two of said cable sections and said gap formingpart being operatively associate with a pressure regulating device incommunication with said melt cavity for regulating the pressure of saidmelt cavity.
 10. The apparatus of claim 9, said gap forming partscomprising a plunger.
 11. The apparatus of claim 9, a second gap formingpart associated with another of said web-forming sections.
 12. Theapparatus of claim 9, said gap forming part being mounted to saidapparatus for reciprocating action with respect to said at least oneweb-forming section.